The functions of the Retrovirus Core are to produce and distribute high titer retrovirus;for use by projects within the F'rogram Project. Specific activities of the core will be to (1) transfect packaging cell lines with various retroviral construct DNA;(2) to harvest, concentrate, and freeze aliquots of retrovirus;(3) to titer each lot of retrovirus;and (4) to distribute retrovirus to each of the projects.